Coke binder oils from dealkylated condensed aromatic tars



April 1969 G. P. HAMNER 3,440,163

COKE BINDER OILS FROM DEALKYLATED CONDENSED AROMATIC TARS Filed Dec. 28, 1965 C4 8| LIGHTER GASES QUENCH FRACTIONATOR LIQUID QUENCH ZONE 9 r SEPARATOR BINDER OIL 3o TO PRODUCT FLUIDIZED COKER 32 STORAGE l6 FOR 3| PRELIMINARY QUENCH \EI/ |5 FEED 7 M /HEATER l2 fil3 COKE GLEN P. HAMMER mvsmoa PATENT ATTORNEY United States. Patent 3,440,163 COKE BINDER OILS FROM DEALKYLATED CONDENSED AROMATIC TARS Glen Porter Hanmer, Baton Rouge, La.., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Dec. 28, 1965, Ser. No. 517,011 Int. Cl. Cc 3/02, 1/20, 1/08 U.S. Cl. 208-40 9 Claims ABSTRACT OF THE DIS'CLOSURE Petroleum or coal tar is dealkylated in a fluid coker. The effluent is heat soaked to convert it to a condensed ring aromatic fraction suitable as a coke binder oil.

This invention relates to the preparation of improved carbonaceous binders for use in preparing carbon or graphite electrodes. More particularly, this invention relates to the preparation of high quality coke binder materials from coal tar or petroleum tar fractions.

Carbon or graphite electrodes are produced from suitably hard carbonaceous materials, such as calcined coke. The coke is calcined to remove volatile materials and reduce shrinkage encountered in the subsequent electrode baking operations. Since coke has no natural adhesiveness, it cannot be formed into a desired shape without the addition of a binder material, usually referred to as a binder oil or pitch because of its consistency. Various amounts of binder oil are utilized depending upon the type of electrode to be manufactured. The prebaked electrode, so called because it is molded and baked at high temperatures, e.g., 18002200 F., for periods of time ranging up to 30 days, before being used as an electrode, usually requires a blend of about 7590 wt. percent coke and 10-25 Wt. percent binder oil. The Soderburg type of electrode requires a blend of about 6085 wt. percent coke and -40 wt. percent binder oil. A greater amount of binder oil is used in the Soderburg electrode to increase the plasticity of the blend. The Soderburg electrode is produced by continuously adding the coke-binder blend at the top of a cell, baking the blend by the heat of the cell, e.g., 1700-1900 F., as it moves downward due to electrode consumption.

Electrode cost is directly related to the life of the electrode, which in turn is dependent upon the quality of the binder material. During use, for example in the electrolytic reduction of alumina to aluminum metal, electrode dusting due to the different rate of consumption of coke particles and binder coke has become a serious problem. The binder coke is the carbonaceous deposit from the binder oil formed during baking of the electrode. The higher rate of consumption of the binder coke relative to the coke particles is attributed to the difference in reactivity between the coke particles and the binder coke. The result is loosening of the coke particles from the electrode before they are fully consumed, thus giving rise to particles of loose coke called dust. This coke dust can short-circuit the electrolysis bath and at best represents lost coke, i.e., coke not used in reducing alumina. The tendency of electrodes to dusting can be greatly decreased with a dense, low porosity electrode structure. To achieve this structure binder material must have physical properties that fall within narrowly specified limits. These properties have been developed empirically, some of the more important factors being: coking properties, softening point, relatively high ratio of aromatic hydrogen to methylene hydrogen, and carbon to hydrogen atomic ratio. Furthermore, the binder material must possess a high Conradson carbon number in conjunction with a satisfactory 3,440,163 Patented Apr. 22, 1969 "ice softening point. The Conradson carbon number, ASTM- D189, is a measure of coking properties and is the Weight percent carbon residue after destructive distillation. The softening point, ASTM-D36-62T, is that temperature at which a steel ball drops through a specific quantity sample suspended in glycerine. Binder oils with softening points below about F. have been found unsatisfactory because of failure to provide sufficient adhesive force, causing the electrode to lose shape. Further, binder oils with softening points above about 290 F. are also unsatisfactory since they do not impart enough plasticity to the coke-binder blend.

To summarize, the desired binder material is one that will lead to satisfactory electrodes and compactions, and has a Conradson carbon content of at least 50 with a softening point in the range of 180290 F. Further, a suitable binder oil will have a high degree of aromaticity, i.e., low amount of methylene hydrogen. Methylene hydrogen must be kept at a minimum since baking (as occurs during electrode formation) releases surplus hydrogen, represented in methylene groups, and results in excessive gassing. This gas formation prevents the electrode from attaining the density desired for electrical conductivity and also leads to a weakened structure. For this desired condition of high aromaticity with low methylene hydrogen the atomic ratio of carbon to hydrogen must be relatively high. A recently developed method for determining the aromatic hydrogen to methylene hydrogen ratio by infrared techniques provides a more reliable measure for predicting the binder material performance than the carbon to hydrogen ratio. The process of this invention provides aromatic hydrogen to methylene hydrogen ratios of greater thanZ, which is a considerable improvement over coal tar binders.

It is known that petroleum pitches do not possess the requisite properties of high Conradson carbon number together with a satisfactory softening point. A petroleum pitch with an adequate Conradson carbon number will normally have a too high softening point. Conversely, a petroleum pitch with a satisfactory softening point will normally have a low Conradson carbon number. As a result, coal tar pitches have been used almost exclusively as the binder material for electrode manufacture.

Since petroleum fractions are less expensive and more readily available than coal tar pitches, industrial process have been developed to upgrade petroleum fractions for use as binder materials. (The increasing requirement for higher quality binder materials has also led to the upgrading of coal tar binder materials.) These processes normally require thermal soaking of the feed stocks, which results in cracking and dealkylation of aromatic fractions. Cracking and dealkylation at temperatures of about 850 F. produce large quantities of coke and carbon residues, i.e., up to 30% or more of the feed. These residues cause fouling of equipment and resultant costly downtime for cleaning. Furthermore, the dealkylation is not complete, i.e., substantial methylene hydrogen remains, leading to gassing when the binder is subsequently baked with the coke to form the electrode.

It is one object of this invention, therefore, to provide a process whereby high quality binder materials, equal to coal tar binder materials, may be produced from petroleum tar fractions. It is another object of this invention to prepare binder materials by a method wherein fouling of process equipment due to coke and carbon residues formed during thermal treatment of feed stocks is eliminated. It is still another object of this invention to provide a process whereby coal tar fractions may be upgraded for use as binder materials. These and other objects will become apparent from the following description of this invention.

In accordance with the present invention, a suitable coal tar or petroleum fraction is thermally dealkylated in a fluidized coke bed at temperatures of 13001600 F. under pressures of -100 p.s.i.g. for about 0.1- seconds. A vaporous product mixture from the fluidized coke bed is separated of any carbonaceous particles entrained therein. (These carbonaceous particles may, if desired, be recycled to the fluidized coke bed.) A portion of the product mixture is then converted to a condensed polynuclear aromatic fraction at temperatures of about 650800 F. for about l6 hours. The condensed aromatic fraction, i.e., the 800 F binder oil, is recovered as the bottoms fraction of a fractionating column wherein the more volatile components of the product mixture, i.e., boiling up to about 800850 F., are separated. Conversion of a portion of the dealkylated feed to a condensed aromatic fraction may be effected by maintaining a high reflux ratio between the fractionating column and its reboiler.

In a preferred embodiment of this invention, a condenser-soaker operating at temperatures of about 650800 F., preferably 700750 F., and under pressures of about 0-100 p.s.i.g., may be utilized to effect a part of or all of the aromatic condensation. The condensed polynuclear aromatic fraction is recovered from the fractionating column and used as a high quality 800 F.+ binder oil.

Binder materials produced in accordance with the above process, from petroleum tar fractions, exhibit properties equal to or better than presently available coal tar binders. The fluid coker thermally cracks the feed and dealkylates the aromatic fractions. The high temperature allows a considerable degree of dealkylation, i.e., greater than 90% of the methylene side chains are removed. Furthermore, the coke and carbon residues formed do not foul the coker because of the nature of this process operation. As coke is formed it may be removed from the fluidized bed and recovered for use in other areas, e.g., burning for fuel to heat the coker. Thus, the process of this invention turns to advantage a previously disadvantageous situation.

Another of the great advantages of this invention is that the selection of a feed stock is in no way critical.

Since this invention is predicated on the improvement of known feed stocks, petroleum feed stocks may be broadly characterized as any petroleum hydrocarbon fraction heavier than 650 F., and preferably 650- 1000 F. These fractions may be derived from a variety of sources, i.e., shale, tar sands, or petroleum tars which can be dealkylated and condensed to form suitable binder materials. This invention is also applicable to the improvement of coal tars. Similarly, any coal tar that can be dealkylated and condensed to form a suitable binder material is also suitable as a feed stock.

The scope of feed stocks contemplated by this invention includes materials such as petroleum residues, not previously desirable, but due to this invention can be considered useful for transformation into binder materials.

Examples of feed stocks suitable for use in the present invention include heavy virgin residual oils which form the bottoms fraction in the distillation of topped crude oil. The heavy virgin residual oils are obtained by delivering the topped crude oil from an atmospheric tower in which, for example, furnace oil and lighter fractions have been removed, to a vacuum tower. A distillate gas oil suitable for use as a catalytic cracking charge stock is discharged from the top of the vacuum tower and a bottoms fraction containing the heavy virgin residual oils is delivered from the bottom of the tower. These fractions include oils boiling above 1000 F.

Another suitable feed stock includes the bottoms fraction obtained from the distillation of cracked oil produced from the catalytic cracking of petroleum gas oils. Cracking is carried out in the presence of catalysts, such as silica-alumina catalysts which are frequently used in the fluidized state. The cracked oil product is then subjected to distillation. The residue or bottoms product of the distillation step is transferred to a slurry settler for catalyst removal. The remaining oil is a suitable feed stock for the process of this invention.

Other petroleum tar fractions available from either thermal or catalytic cracking may be utilized as feeds to a steam cracker for production of a suitable tar feed. The bottoms fraction of a fractionator for steam-cracked products may also make up the feed for this process. The bottoms fraction includes those fractions boiling above 650 F.

A particularly preferred feed is the petroleum residue from mid-boiling fractions processed by the following sequence of operations: (1) catalytic cracking of a midboiling petroleum fraction in which naphthas and isoparaflins are largely converted; trace impurities such as nitrogen, sulfur, and metals are also removed; (2) the resulting product is steam cracked at 1200-1500 F. wherein straight chain paraffins are converted for use as basic chemical raw materials; (3) the high boiling aromatics and condensation products are recovered from the steam cracker products as tar.

Another particularly preferred feed stock and one found to yield a suitable pitch is the tar bottoms fraction obtained from the distillation of cracked oil produced by steam cracking light or heavy catalytic cycle oils at 1200-1500 F. The tar material from the steam cracker is distilled at temperatures below about 650 F. at pressures of 520 p.s.i.g. The residue, highly aromatic tar bottoms, of the distillation process may be employed as a particularly suitable feed stock for this process.

Coal tar pitch may also be employed as a feed stock. In general, any suitable coal tar pitch which is comprised of complex polynuclear aromatic compounds containing phenolic groups, amino groups or other active hydrogen groups may be used as a feed stock for the process of this invention. The consistency of the pitch may vary from that of a light tar up to a heavy tar and Will have softening points of about 250 F.

Coal tar oils boiling in the range 500850 F. are a particularly preferred coal tar stock. These oils are prepared by the distillation of a total coal tar fraction produced from low temperature and/or high temperature coking of coal.

Although the present invention will be described with reference to steam-cracked heavy catalytic cycle oil, it is to be understood that any suitable feed stock, particularly those set forth above, may be utilized.

Shale oil produced by retorting of shale at 900- 1200 F. to yield an organic oil of 650 F.+ boiling range may also be used as a feed stock. When processing such a feed increased gaseous products such as NH and other light gaseous products are produced during the dealkylation operation. Impurities such as nitrogen and ash components are generally removed from the total shale oil such that a 1000 F. and lighter oil fraction free of such impurities is the desired shale oil fraction which is used as feed to the process of this invention.

Similarly, oil fractions of 650F.+ boiling point which are of ash materials, may be produced from Canadian tar sands by a retorting process described for the shale retorting operation above.

The operation of the present invention will be best understood and appreciated from the following description of the process with reference to the attached drawing.

FIGURE 1 is a typical flowplan, schematically illustrating a continuous process for production of binder oils.

Turning now to the drawing, coal or petroleum tar feed stock, e.g., heavy catalytic cycle oil, transferred directly from a steam cracker or a suitable storage tank (not shown) is delivered to a fluidized bed of coke in coker reactor 16 by feed stream 10. Fluidized coker 16 is preferably operated at temperatures of about 1400- 1500 F., but may be operated at temperatures ranging from about 1300 F. to about 1600 F. The pressure in coker reactor 16 is not critical and may vary from 0 to about 100 p.s.i.g. Residence time will generally be from about 0.1 to about seconds, and preferably 0.5 -5 seconds. The feed is normally sprayed directly into the coke bed by a plurality of nozzles (not shown) located within coker reactor 16. The feed stock covers the coke particles, immediately cracking, dealkylating, and vaporizing. A solid residue of coke and carbon black is formed and remains in the fluid coke bed.

Heat for the coker reactor is supplied by continuously transferring coke particles by Way of line 12 to heater 14, line 15 and then back to coker reactor 16. The heat is generated entirely within heater 14 and can be supplied by burning of a portion of the coke itself. Oxygen or an oxygen-containing gas, such as air, is supplied to heater 14 via line 13 for combustion purposes. If it is desired to conserve the coke product, such as in an operation wherein coke is a by-product of this process, the heat may be generated by burning a hydrocarbon fuel in heater 14, thereby heating the coke as it passes through the heater and back to the coker reactor.

The tendency of coke and carbon residues to foul equipment, normally associated with low temperature, e.g., below about 900 F., liquid phase thermal treatments is completely eliminated. Furthermore, the formation of the residue is used to advantage. Excess coke and carbon reisdue, when produced from a low sulfur, ashfree hydrocarbon fraction, such as 650l000 F. fraction type feeds, may be withdrawn from the bottom of coker reactor 16 as premium high quality coke by line 11.

The coker reactor can be operated with or without a fluidizing gas. If a fluidizing gas is utilized, it is injected at the bottom of the coker reactor and withdrawn at the top of the coker reactor through line 17 with the vaporized products of the reaction. Gases such as carbon dioxide, steam, nitrogen, or other gases, inert to the reaction, may be used. When a fluidizing gas is not utilized, partial or complete vaporization of the feed stock serves to fluidize the coke bed.

Products of coker reactor 16 are passed to a cyclone separator 18, or equivalent, via line 17, to separate out entrained solids in the vaporous product mixture. Such solids are returned to the coker by line 19.

In an embodiment of this invention, the high temperature gaseous product of separator 18 is introduced to a quench zone 21, via line 20. A suitable method for quenching the gaseous product in line 20 is to pass the vapors through a venturi shaped throat, thereby increasing the velocity of the vapor stream. The high velocity vapor stream is then discharged into the center of a conduit having approximately twice the cross sectional area of the throat. A quench liquid, such as naphtha or recycle of a mid range boiling fraction such as may be recovered from fractionating column 27, is introduced tangentially into this larger diameter conduit at a point approximately one-third of a pipe diameter past the point of expansion. The high velocity vapor stream draws the quench liquid along the walls of the conduit and up into the vapor stream; thus, providing rapid and eflicient contacting of the hot vapors with the quench liquid. The quench liquid should be introduced at relatively low velocities in order to simulate annular flow in the quench zone.

The quench zone 21 is generally employed to reduce the temperature of the product stream of line 20 to about 700-900 F. Therefore, quench liquid temperatures of about 350-650 F. may normally be used. Variations of the operation of this quench zone to produce the most effective cooling will be obvious to those skilled in the art and this invention is not to be limited to the quench method described.

It should be understood that quench zone 21 is not an essential part of this invention. Cooling of the vaporous product mixture from coker reactor 16 may take place entirely in condenser-soaker 23. However, when such is the case, large amounts of coolant will usually be required to reduce the temperature of the product stream to the desired range.

The product of the quench zone containing some condensed oils and vapors passes by way of line 22 to condenser-soaker 23. Condenser-soaker 23 is maintained at temperatures of about 650-800" F., and preferably at 700750 F., under pressures of about 0-100 p.s.i.g., but lower pressures than in the reactor coker 16. C and lighter gases are flashed off from condenser-soaker 23 by way of line 25. Steam supplied from line 24 may be used to aid in quenching the product to the desired temperature, if necessary. The steam may be injected directly with quench oil, into the product mixture, or quenching may be effected by heat exchanger methods. The product may remain in condenser-soaker 23 for about l-6 hours, thereby converting the dealkylated aromatic oil fraction to a condensed polynuclear aromatic fraction.

The liquid product of condenser-'soaker 23, containing a mixture of highly aromatic binder oil, light hydrocarbons, and dealkylated feed is transferred to a fractionating column 27 by line 26. Generally, the fractionating column will operate at a bottoms temperature of about 650900 F., and preferably 700-850 F., under pressures of less than one atmosphere to about p.s.i.g. Further aromatic condensation may occur in the reboiler (not shown) of the fractionating column by maintaining a high reflux ratio of the bottoms fraction. Steam injection to the tower allows operation at lower pressures and temperatures. An overhead fraction of C 430 F. boiling range is removed by line 28 for use as chemical raw materials or for blending in motor gasolines. An intermediate fraction boiling in the range of about 430825 F. is removed by line 29 for recycle to the process, use as a quench oil for lowering coker reactor product temperature in quench zone 21, or for specialty uses and chemical raw materials. The condensed aromatic fraction is recovered as binder oil from the bottoms by line 30 and transferred to product storage.

In another embodiment of this invention, a portion or all of the binder oil product may be transferred, by line 32, to aid in cooling product stream 20 before stream 20 enters quench zone 21. The binder oil is then passed to product storage by line 31. Use of the binder oil as a preliminary quench will further reduce the amount of coolant required in quench zone 21 and condenser-soaker 23.

The following examples further illustrate this invention and are not to be considered as limiting this invention in any way.

EXAMPLE 1 A feed stock comprising steam cracked tar from processing catalytic cycle oil stock boiling in the range 550875 F. was subjected to the process of this invention. The following tables show the results.

Table I.--Feed inspections Specific gravity 60 F. 1.06 Conradson carbon number, wt. percent 3 Sulfur, wt. percent 1 Oxygen, wt. percent 0.01 Aromatic hydrogen/methylene hydrogen 0.37

Carbon, wt. percent 92.61

Hydrogen, wt. percent 6.53

Table II.Pr0cess conditions in coker Temperature, F. l450-1500 Pressure, p.s.i.g 8 Residence time, sec. 1-3 Fluidizing gas, N CF/hr 50 Feed, ml./hr. 1000 7 Table III.-Prduct distribution (ex N gas) C and lighter, wt. percent 16.2 400 F.+ liquid, wt. percent 47.4 Coke+carbon black, wt. percent 36.4

Table IV.l/1specti0ns on liquid product Specific gravity 60 F. 1.14 C 430 F., wt. percent 2.1 430-825 F., wt. percent 68.6 Binder oil, wt. percent 29.3

Table V.Inspecti0ns on binder il Softening point, F. 214 Conradson carbon number, wt. percent 54.8 Carbon, wt. percent 94.13 Hydrogen, wt. percent 4.69 Carbon/hydrogen 1.67 Aromatic hydrogen/methylene hydrogen 4.13 Oxygen, wt. percent 0.06

EXAMPLE 2 Feed stock similar to that used in Example 1 was processed by the method of this invention. Similar feed stock was thermally soaked at 830 F. to prepare binder oil. Table VI compares the properties.

TABLE VI.COMPARSION OF PROCESSES Since a minimum Conradson Carbon number of 50 is required, it is obvious that the lower temperature process does not produce a satisfactory binder oil. Also, the very large difference in the aromatic hydrogen/methylene hydrogen ratio shows that a binder oil produced by the present method when employed as a binder for electrode production will yield considerably less gassing and a denser structure.

EXAMPLE 3 Table VII shows the comparison of the binder oil produced in Example 1 with coal tar stocks presently available as binder materials.

TABLE VII.--COMPARISON OF PETROLEUM BINDER OIL AND COAL TAR Binder Inspections Petroleum Coal Tar Softening point, F. 214 215 Carbon, weight percent 94. 13 92. 76 Hydrogen, weight percent 4. G9 4. 32 Aromatic hydrogen/methylene hydrogen. 4.13 1.8 Carbon/hydrogen 1. 67 1. 79 Oxygen, weight percent.. 0. 06 1. 33 Nitrogen, weight percent 1. 0 Sulfur, weight percent.--" 1. 0 0.5 Ash, weight percent O) 0 03 Nil.

What is claimed is:

1. A process for preparing binder oil from a feed stock selected from the group consisting of petroleum tar hydrocarbon fractions boiling from about 6501000 F. and coal tar fractions which comprises dealkylating said feed stock in a fluidized coke bed at temperatures of about l3001600 F., under pressures of about 0l00 p.s.i.g., for about 01-10 seconds; recovering a dealkylated vaporous mixture product mixture from said fluidized coke bed; converting a portion of said product mixture to a condensed aromatic fraction at temperatures of about 650- 800 F. for about 1-6 hours; fractionating said product mixture; and, recovering the condensed aromatic fraction consisting essentially of 800 F.+ material as binder oil from the bottoms of said fractionator.

2. The process of claim 1 wherein an inert fluidizing gas is used to fluidize the coke bed.

3. The process of claim 1 wherein said feed stock is dealkylated at temperatures of 1400-1500 F.

4. The process of claim 1 wherein the residence time of said feed stock in said fluidized coke bed is 0.5-5.0 seconds.

5. The process of claim 1 wherein said product mixture is converted to said condensed aromatic fraction at temperatures of 700750 F.

6. The process of claim 1 wherein said fractionating column operates at a bottom temperature of 650900 F.

7. A process for preparing binder oil from a feed stock comprising petroleum tar hydrocarbon fractions boiling from 650-1000 P. which comprises dealkylating said feed stock in a fluidized coke bed at temperatures of 13001600 F., under pressures of 0100 p.s.i.g. for 0.1- 10 seconds; recovering a dealkylated vaporous product mixture from said fluidized coke bed; quenching said product mixture to about 700900 F. in a quench zone; converting a portion of said product mixture to a condensed aromatic fraction at temperatures of 650800 F. for 1-6 hours; fractionating said product mixture in a fractionating column with a bottoms temperature of 650- 900 F.; and, recovering said condensed aromatic fraction consisting essentially of 800 F.+ material as binder oil from the bottoms of said fractionating column.

8. The process of claim 7 wherein said feed stock is a petroleum tar fraction resulting from the steam cracking of catalytic cycle oil.

9. The method of claim 7 wherein said product mixture is quenched by injecting a 350650 F. quench oil directly into said product mixture in said quench zone.

References Cited UNITED STATES PATENTS 2,893,946 7/1959 Brown 208-127 2,922,755 1/1960 Hackley 20839 3,140,248 7/ 1964 Bell et al. 208-40 HERBERT LEVINE, Primary Examiner.

US. Cl. X.R. 

